1. Field of the Invention
The present invention relates to the opening of large vessels which operate under high temperatures and particularly to coke drums.
2. Brief Description of Relevant Art
Petroleum refining operations, in which crude oil is processed to produce gasoline, diesel fuel, lubricants and the like, always produce residues that are referred to in the industry as "coke."Coke residue, also termed "coke feedstock," is usually heated in a furnace to cause destructive distillation in which substantially all of the remaining useable hydrocarbon products are derived from the residue leaving the coke product, essentially carbon, which is conveyed into a coke drum. The typical coke drum is a large, upright, cylindrical, steel walled vessel that may, for example, be on the order of approximately 90-100 feet in height (30.48 meters) and 20-30 feet in diameter (6.10-9.14 meters), although the actual structural size and shape of the coke drum can vary considerably from one installation to another.
Typically, a refinery has a plurality of coke drums. The production of coke is usually a batch process, that is, coke feedstock is deposited into a coke drum as a liquid slurry in a very hot state--temperatures of about 900 degrees Fahrenheit (477.4 degrees Centigrade). The coke may be solid, spongy, shot or pellet-like, or even viscous liquid, depending on the quality and composition of the feedstock. When the drum is full, the feed is diverted to an empty drum and the coke filled drum is steam purged and cooled with quench water. The drum is then drained of water and the top and bottom heads of the drum are removed for removing the coke from the drum. After the coke is removed, the drum is ready to be placed back in service to repeat the cycle. While coke is being cooled in one or more drums and while the cooled coke is being extracted from one or more drums, other drums are employed to receive the continuous production of coke feedstock as a part of the refining process.
How the coke is removed from a drum varies with the type and consistency of the coke. For example, solid coke may have to be drilled out whereas shot and liquid coke may fall out when the drum bottom head is removed. Even with steam purging and cooling with quench water, however, the coke is at a high temperature, typically exceeding 200 degrees Fahrenheit, when the drum heads are opened. The drum is also under pressure. When the drum is opened, hot steam and some hot coke typically pour out with force. For safety, the drum heads are opened remotely and the drum has a head or cover assembly suited for remote operation. An example of a suitable remotely operable vessel cover particularly useful for a coke drum is described in U.S. Pat. No. 5,221,019, assigned to Hahn and Clay in Houston, Tex., and an example of a deheading or unheading device for remotely removing such a vessel cover is described in Hahn and Clay's "FACT System.RTM." brochure.
Working in the vicinity of the bottom head of a coke drum is potentially hazardous, particularly prior to coke removal. Water and other materials can unexpectedly fall out of a drum, especially in the case of a coke cave-in. Additional methods and equipment have been introduced and proposed to further automate removal of coke from coke drums and to enhance safety measures for workers in the vicinity of the drums. Because of the high temperatures and pressures associated with the drums, such automatic equipment in proximity to the drums will also be exposed to high temperatures and pressures. Such high temperatures and pressures cause stress on the equipment and can significantly shorten their useable life. A need continues to exist for safer methods for removing high temperature materials from large industrial vessels such as coke drums.